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Some is undoubtedly "poison." The Journal carried a story a while back about some Citadel deals that were crafted with, shall we say, dubious quality.
But the problem is that no one cares to price the nuts and bolts; the market for cdo's lacks the very basic requirement of transparency (at the moment) and so it's fraught with superstition. It's an evironment made for hucksters of every stripe.